Crane limit switch



R. B. HUNTER CRANE LIMIT SWITCH 4March 16, 1943.

Filed sept. 2o, 1941' 2 Sheets-Sheet 1 March 16, 1943. R, B lulu-nin` 2,313,995

CRANE LIMIT SWITCH` Filed Sept. V2O, 1941 2 Sheets-Sheet 2 Petenied Mer. 1,6, 1943 UNITED STATES PATENT OFFICE: d i `2,313,995

f A VcnilNnmrn'r SWITCH menare rs. Hunter, snerewoea, wie., einer te Cutler-Hammer, Inc., Milwaukee, Wis., a corl poration of Delaware 'v n Y Application september zo, 1941, serial Ne.` meer This invention relates to an imirovement in crane limit switches.

crane limit switches are installed pn electrically operated cranes and hoists for the purpose of which has along operating life, and which is not d likely to get outof order. Y

Another object is to provide Va limit 4switch which may be mounted in various angular posidisconnecting the motor from the line and bring- 5 tions, while insuring reliable operation and maining it to., a quick stop, if ,the hook of the hoist tenance of its insulation. should tend to overtravel its safe upper limit.- I( Another object is to provide an improved the hook is permitted to overtravel, the motor puts mounting and arrangement Of the Current eerry' an excessive strain on the hoisting cables, or the ing parts of limit switches. hook and load interfere with parts of the hoist, AnOtheI Object 1S t0 provide a maximum 0f which may cause the cable to part and release the Creepage distende between Conducting Parts Of hook and load resulting in great damage and dierent polarity of the limit switch. endangering life, Another object is to provide a limit switch, in The overtravel referred to might be due to which the insulating resistance between live various causes, such as failure of the operator to i parts 0f different Potentials 1S nOt Substantially disconnect the motor by the centmner at the reduced by the accumulation of dust and the like. proper instant, or the controller may become AIlOther- Object iS t0 provide a limit switch ineffective and fail to disconnect the motor. .or which will continue to operate satisfactorily even Seme dimculty may devemp 1n the effen compuafter the failure of certain operating elements. cated and exposed wiring of the system. Another object is to provide a counterweightfor For the aforementioned reasons it is highly e limit SWteh With an adjustable means for desirame to provide a limit switchV which wi11 not engagement by the hoisting tackle and the ropes. -fail either electrically or mechanically to dis- Another Object 1S tO Provide emeient and Safe connect the motor under any circumstances. A y. guide means for the eountelweightgreat many constructions have been proposed 'in 25 Various Other ObjeOtS and advantages Of the the past, butnone of these has fully met al1 of the invention Will hereinafter dl-'Dedlexacting requ'jremente 'I'he accompanying drawings illustrate an em- A commercial limit switch mustbe adapted'for bodiment 0f the invention Which Will n0W be mounting in various gula-positions, depending described, it being understood that the illustrated upon the mechanical arrangement ofthe hoisting embodlment n lay be modified m Various Ways machinery. The construction should therefore Vitiup departme from the Scope 0f the appended be such that the switch is readily rearranged for c a s' the various modes of mountings. Furthermore the drawings Figure -1 is e plan View 0f e' the limit switch is usually mounted in a rather limit switch embodying the invention-the cover inaccessible location and therefore may receive mxilbe; teing onttedl i little attention. In many places, such as foun- Fig s a sec Ona' .V ew on the une 2-*2 0f dries and the like, it is exposed to a great deal of f V dust, which Vmay seriously aiect its electrical 3 1S a' sectional View on the une 3 3 of insulation, while periodic cleaning of the switch I to remove the dust cannot be relied upon, and is 40 cer'. :t gragglglslgon through the in any eveflten undesirable burden: Fig. 5 is an exterior end view of the limit Most limit switches are equipped with switch and weight, which biases them to their normal pesr- Fig. 6 is a diagram of connections, illustrative tien and Wnlen 1S lifted by the heen 0r lnevmg 45 of an appli tion oi the limit switch to control of sheave for operation. The usual weight 1s susa direct c ent motor. pended by a rope which may tangle with the Referring to the drawings'-the cntact mecha hoisting TOPeS and Cause damage nism of the limit switch is enclosed in a frame I, The object of the Present invention iS t0 prO- provided with a removable end cover 2; Pivotally vide a simple and imPI'OVed limit Switch, which 50 supported by theframe and cover is lan operating meets the aforementioned exacting requirements shaft 3, which throughout the major portions of and which avoids the disadvantages of Yprier art its length is of square cross section. switches. The switching mechanism is provided withsta- Another object is to provide a simple and imtionary contact blocks l. having removable conproved linut switch snap operating' mechanism 55` tact tips 5. The stationary contact blocks are mounted in pairs syrmetrical with respect to the operating shaft 3, on insulating blocks 6. 'Ihese insulating blocks are substantially rectangular in cross section and are arranged with their major axes transverse to the operating shaft 3, and each insulating block is in turn attached to the frame I by means of a pair of insulating spacers 'I. To further increase the creepage distance between the two contact blocks 4 of each pair along the surface of the blocks 6, a number of transverse notches 6' (Fig. 2) may be cut into that side of each block 6 to which the contact blocks 4 are attached.

As the limit switch is usually mounted in the horizontal position shown in Figs. 2 and 3, it is desirable to arrange that the creepage distance between live parts of different polarity be as great as possible, and that horizontal surfaces upon which dust might collect, and which would reduce the surface insulation between live parts, be avoided, or be made as long as possible, and to intersperse between such horizontal surfaces (by providing notches or shoulders) vertical surfaces upon which dust cannot accumulate. The arrangement should be such that these conditions obtain with the limit switch mounted in any angular position around the horizontal shaft. The aforementioned requirements are met by the construction and the 4mounting of the stationary contacts and supports as aforedescribed.

Each stationary contact'block 4 is fastened to the respective mounting block 6 by means of two bolts 8, which engage special nuts 9 of cylindrical shape, inserted in suitable holes drilled transversely through the mounting block 8, the latter being of substantially rectangular form in cross section, as aforestated. Each mounting block 6 is in turn mounted upon the pair of spacing blocks 'I by bolts III which cooperatively engage cylindrical nuts I I, inserted in suitable holes drilled transversely through the blocks 'I, the arrangement of the bolts I and the nuts yII being similar to that of the bolts 8 and the nuts 9. The blocks 'I are fastened to the frame I by means of screw boltsu I2, the heads of which are countersunk in the blocks 1, as shown in dotted lines at I3, while the threaded ends of the bolts I2 cooperatively engage tapped openings or recesses in the frame I.

From the foregoing, it will be seen that the creepage surface between each nut 9 which has the same potential as its associated contact block 4 and the bolt I2 which is of the same potential as the frame I is exceedingly large, and that a large cross section of the dielectric of the block 6 is in the path between the two parts, and that there is no direct horizontal creepage surface between any live part connected to the block 4 and the frame I for any positioning of the limit switch.

Referring now to the movable contacts, the same are mounted in pairs upon brackets I4 attached to and insulated from the shaft 3 adjacent to the respective pairs of stationary contact tips 5. Each bracket I4 is fastened to shaft 3 by means of a clamping piece I5, and is insulated therefrom by an insulating tube I6. Pivotally mounted 4to each bracket I4 ,is a pair of contact supports I1, each carrying a renewable contact tip I8. Attached to each contact support I1 is one end of a flexible connector I9, the other end of which is fastened to a terminal bolt which passes transversely throughvthe insulating'block t. The contact supports II with their attached tips I8 are biased toward the stationary contact asians A tips l by means of springs 2| and have their outward movement limited by stop pins 2 2 carried by said brackets I4.

Mounted upon the insulating tube I I on both sides of the brackets I4 are pairs of insulating collars 23, between each pair of which is further mounted an insulating disk or plate 24, the purpose of which insulating parts is to increase the creepage surface between adjacent brackets I4, and between the brackets and grounded parts near the ends of the shaft, and particularly to interpose vertical creepage. surfaces between the various live parts of different polarity.

The circuit connections of the apparatus thus far described, for a direct current series motor, are illustrated in Fig. 6. In this drawing only the connections essential to explain the operation of the device are shown, whereas the conventional control apparatus for varying the speed and direction of rotation of the motor is not shown, these being of any one of a number of well known types. As shown in Fig. 6, circuit is established from the positive line to one terminal of the series field and a branch extends to' stationary contact 5, The other terminal of the series field is connected to stationary contact 5b, and is also connected to stationary contact 5 which is symmetrical to contact 5* with respect to the shaft 3. A fourth stationary contact 5d is connected to the negative line terminal. One terminal of the armature is connected to' one of the brackets I4* which carries the movable contacts I8l and Il, while the other terminal of the motor armature isconnected to another bracket I4, which carries the movable contacts I l and Il. The contacts Il, I Ib, II and Ild cooperate with the contacts le, il?, 5 and i, respectively.

In the normal operating position, shown in Fig. 6, the movable and stationary contacts at the left-hand side of the' shaft'l are respectivelyen- Swed with each other, and therefore a current flows from the positive line through the motor eld, contacts 5, II and bracket I4* through the motor armature and through bracket I4? and contacts Iliand'i -to th'enegative'fside of the line. lWhen the limit of travel .for the motor is reached, the shaft l is rotated in a clockwise direction, as will be explained more in detail hereinafter, whereupon. the contacts-to the left of the operating shaft in Fig. 6 are opened and the contacts to the nght thereof are closed. The current then flows through the series field, con-'- tacts I, IIb and bracket I4 through the armature in a direction opposite to that in which it flows under normal conditions, thence through bracket I4", contacts Il* and 5* back to the series field. The full line arrows in Fig. 6 show the direction of current ilow under normal conditions, whereas the arrows in dotted lines show the direction of flow for braking. Under braking conditions the motor functions as a simple series wound generator and comes to a standstill in the usual manner.

The mechanism for operating tno snort a will now be described, with reference to Figs. 1 and 5.

A lever 2l (one end 2t of which is made in the form of a heavy counterweight, whereas the other f end is provided with a perforated ear 2l, for the attachment of a weight 2l, Hg. 5, by means of a cable 29) is keyed at its center (see Figs. 1 and 4) to a shaft extension 3|* of a casting. The shaft extension Il* is Supported for rotary motion by a ball bearing II (Fig. 4) in the end cover 2. The weight 29 overthe counterweight 2l, so that normally the weight 2l biases the shaft to the position shown in Fig. 5. n, Y

however, the limit of travel is reached, the weight 23 is` lifted by a suitable mechanism ,driven by the motor Vwhich is controlled by the limit switch.

i This permits the weight 23 to rotate the casting deredcylindrical end portion 33 of the shaft 3.

A ball bearing 34, provides for free relative rotary movement between the casting 30 and the shaft 3. The casting 30 is also provided with an arm 35 upon which is mounted a cylindrical guide member 33, one end of which passes through a hole 31 formed in a double ended lever 33, which llatter is pivotally supported aty 33 on a second arm 40 of the casting 30. A spring 4I surrounds the cylindrical guide 35, its ends respectively abutting the arm 35 and lever 33 so that the spring is always compressed to at least a predetermined degree, thus tending to rotate the vlever 33 counterclockwise and to urge a roller 42, mounted on the second arm 33" of the lever 33, toward the center of the shaft 3. Mounted on a square portion of theshaft 3, adjacent to the bearing 34, and in alinement with the roller 42, is a cam member 43 (Figs. 3 and 4) which is engaged by the roller 42 (see Fig. 3). Secured to the inner face of the end cover 2 on one side of the center of shaft 3. as by means of a pair of bolts- 44, 44", is a casting 44, which is arranged to conflne a helical spring 45. The spring 45 isfurther. so arranged, that its ends may be engaged by' arms 45 and 41, respectively, of the casting 30, to limit the oscillation thereof and to absorb its impact.

It will be seen that when the casting 30 is rotated counterclockwise (Figs. 3 and 5) by the lifting of the weight 23, the spring 4I is compressed and roller 42 rides down on the left side of the cam 43 (Fig. 3) until it passes its apex, whereupon the cam is caused to rotate with a snap action in a clockwise direction (Fig. 3) to effect engagement of contacts I3L and I8b with contacts 5' and tib (Fig. 6). AThe energy stored up in the counterweight 26 of lever 25 is absorbed by the spring 45, as the arm 46 moves away from the latter (Fig. 3) and the arm 41 makes contact therewith. Thus it will be seen that after the roller 42 has moved to the right beyond the apex of cam 43 the movement of shaft 3 is very rapid, and the normally closed contacts (I3,5c and .I 3d, d) of the. switch (Fig. 6) are rapidly opened, and the normally open contacts U3, 5a and I3", 5b) are rapidly closed, thereby reducing to a minimum the amount of arcing between these movable and stationary contacts. This snap action is effected regardless of the speed of upward movement of the weight 23, as will be apparent, thus insuring immediate initiation of the braking action subsequent to interruption of the hoisting power. v

The momentum of the shaft 3, and of the parts connected thereto and moving therewith, is absorbed by a pair of springs 43 which are mounted on a stud 49, which in turn is supported by a lug .53 on the'frame I. The stud 43 bears at its end two collars 5I (Figs. 1 and 2) which maintain the respective springs 48 under some comprese sion. The shaft 3 has fastened thereto a pair f arms 52 which respectively engage with oneor the other of the collars 5I, depending upon the position of shaft 3. Thus when the shaft is moved from one extreme position to the other,

one of the arms 52 makes contact with the collar 5I, respectively associated therewith, thereby compressing thecorresponding spring 43 which thus cushions the impact of the shaft 3.

It should be pointed out that the spring 4I which is subject to relatively great strains, is arranged in such a manner that if it should break.

at one pointV intermediateof its length, its pressure is not completely released, as it is compressed in the normal position to a degree greater than the axial dimension of one coil or convolution thereof, thus insuring that there is still force available to operate the shaft. At the same time y the cylindrical guide 33 (Fig. 3) prevents the spring 4I from dropping out of position. The spring 45 is enclosed in the cage-like structure 0f casting 44. so that it is het easily displaced;4

and springs 43 are confined by the collars 5I attached to stud 43 to preventthem from dropping out of position.

'I'he weight 23 is of generally rectangular shape.

the ropes 55 of the hoisting tackle, so as to pre-` vent the weight from swinging and/or rotating. By using two guides on opposite sides of the weight any substantial lateral movement or rotation of the weight is avoided, and by making the forks adjustable the weight 23 may be readily adapted for various spacings of the hoist tackles. thus further adapting the limit switch for a great variety of conditions met with in its installation.

To mount the limit switch in any other angular position around thecenter of the operating shaft it is only necessary to fasten the lever 25 to the shaft extension 3l) in the corresponding relation, two or more keyways being preferably provided in said shaft extension 30 and in weight lever 25 for this purpose.

Referring again to spring 4|, it is to be understood that the wire employed in forming the same is of such diameter and strength, the initial degree of compression thereof when in assembled position is of such-magnitude, and the pitch of the coils thereof is of such value, as to insure against telescoping of one section thereof into the other, in the event of breakage of the same when in use. By this means snap operation of the shaft 3 by the action of roller 42 upon cam member 43 will be insured in the event of a single break in such spring, the cylindrical guide 35 acting to insure maintenance of all coils of the spring in a coaxial relationship under such a condition.

I claim:

1. A crane limit switch for mounting withY its operating shaft horizontal and for mounting in dierent positions about the axis of its operating shaft comprising, an enclosing casing, an operating shaft oscillatably supported by said casing, a plurality of movable contacts mounted on said shaft, a plurality of pairs of stationary contacts, the stationary contacts of each pair being arranged for selective engagement by one of saidY movable contacts, an elongated insulating supporting block'for each pair of stationary contacts, said block being substantially a rectangular prism with its major axis arranged at a right angle to theaxis of said shaft, means to support said stationary contacts on said insulating tween a normal anda braking position, and including a counterweight for biasing said shaft to its normal position, said counterweight being operable to permit notation of said shaft to its braking position and including adjustable means for engagement with the operating ropes of a crane.

2. A crane limit switch for mounting with its operating shaft horizontal and for mounting in different positions about the axis of its operating shaft comprising, an enclosing casing, an operating shaft oscillatably supported by said casing, a plurality of movable contacts mounted on said shaft, a plurality of Vpairs of stationary contacts, the stationary contacts of each pair being arranged for selective engagement by one of said movable contacts, an elongated insulating supporting block for each pair of stationary contacts, said block being substantially a rectangular prism with its major axis arranged at a right angle to the axis of said shaft, means to support said stationary contacts on said insulating block, an insulatingl spacer interposed between each end of said block and said casing, means'to attach said insulating block to said spacers, means to attach said spacers to said casing, said supporting means, said spacersand said attaching means being arranged to interpose a maximum of vertical insulating surface distance'between any two of said stationary contacts, and between any one of said stationary contacts and said casing with the switch mounted in any of said positions, and a snap action mechanism for oscillating .said shaft between a normal and a braking position, and including a counterweight for biasing said shaft to its normal position, said counterweight being operable to permit rotation of said shaft to its braking position and including adjustable means for engagement with the operating ropes of a crane.

3. A crane limit switch for mounting with its operable to erect s bias or said shaft to its bnring position and including adjustable means for engagement with the operating ropes of a crane.

4. A crane limit switch comprising, in combination with an oscillatable shaft, an operating lever oscillatably mounted concentric with said shaft and biased to a given position, a counterweight connected with said lever and normally exerting a force thereon opposing its normal bias and biasing it to another position,a caml on said shaft having a center apex, a double-ended supporting lever plvotally connected with said operating lever eccentric of its center of rotation, a roller on one arm of said supporting lever operating shaft horizontal and for mounting in different positions about the axis of its operating shaft comprising, an enclosing casing, an operating shaft oscillatably supported by said casing, a plurality of movable contacts mounted on said shaft, a plurality of pairs of stationary contacts,

the stationary contacts of each pair being ar` ranged for selective engagement by one of said movable contacts, an elongated insulating supo porting block for each pair of stationary contacts, each of said supports being substantially a rectangular prism with its maior axis arranged at a right angle to the axis of said shaft, means to support said stationary contacts on said insulating blocks and said blocks on said casing and arranged to interpose a maximum of vertical insulating surface distance between any two of said stationary contacts and between any one of said stationary contacts and said casing with the switch mounted in any of said positions, a snap acting mechanism for oscillating said shaft between a normal and a braking position, buffer means on said casing and said shaft and arranged to stop said shaft in either of its extreme positions and to absorb-the impact due to the action of said snap acting mechanism, and including a counterweight for biasing said shaft to its normal position, said counterweight being and arranged to urge said roller into contactv with said cam.

5. A crane limit switch comprising, in combination with `an oscillatable shaft, an operating lever oscillatably mounted concentric with said shaft and biased to a given position, a weight associated with said lever and normally exerting a force thereon opposing its normal bias and biasing it to another position, a cam on said shaft having a center apex, a double-ended supporting lever pivotally connected with said operating lever eccentric of its center of rotation, a roller on one arm of said supporting lever adapted to engage said cam to bias said shaft to either of its extreme positions of oscillation, -an abutment on said operating lever, .a coiled compression spring interposed between said abutment and the other arm of said supporting lever and arranged to'urge said roller into contact with said cam, and a guide member inside of said spring, said guide member being carried by said abutment and slldable through an orifice in said other arm of said supporting lever. 6.v A crane limit switch comprising, in combination with an oscillatable shaft, an operating lever oscillatably mounted concentric with said shaft and ,biased to a given position, a weight associated with said lever and normally exerting a force thereon opposing its normal bias and biasing it to another position, a cam on said shaft having a central apex, a double-ended supporting lever pivotally connected with said g operating lever eccentric of its centerl of rotation, a roller on one arm of said supporting lever adapted to engage said cam to bias-said shaft to either of its extremepositions of oscillation, an abutment-on said operating lever. a coiled compression springV interposed vbetween said abutment and a second abutment on the other arm of said supporting lever and arranged to urge said roller into contact with said cam, a guide member inside of said spring and movable longitudinally with respect thereto, said guide member being carried by one of said abutments and slldable through an orifice provided in the other of the same, a buffer compression spring having its exds normally conned between stationary abutments, and a pair of spaced abutments on said operating lever adapted to selectively engage the ends of said buffer spring to yieldably stop said lever in its respective opposite extreme positions an to absorb the impact of the latter.

7. A limit switch for controlling the operation of a crane, comprising a snap action mechanism including a weight for biasing said mechanism to a given position and adapted to be moved in response to movementI of an element of said crane to remove said bias, and a pair of guide members each vhaving a loop at one end and extending an adjustable distance from opposing vertical sides of said weight, and each adapted for the free passage of a hoist cable through the respective loop.

8. A limit switch for controlling the operation of a crane, comprising a snap action mechanism including a weight for biasing said mechanism to a given position, and adapted to be moved in responsey to movement of an element of said crane to remove said bias, and a pair of guide forks each having its closed end extending an adjustable distance from one of the opposite vertical sides of said weight and each of said closed ends being adapted for the free passage of a hoist cable therethrough.

9. A crane limit switch for mounting with its operating shaft horizontal and for mounting in different positions about the axis of its operating shaft comprising, a metal enclosing casing, an operating shaft .oscillatably supported by said casing, a plurality of pairs of movable contacts mounted on said shaft in insulated relationship thereto, the movable contacts of each pair being electrically connected with each other, a corresponding number of pairs of stationary contacts, one stationary contact of each pair being arranged for engagement simultaneously by the movable contacts respectively associated therewith, a relatively long insulating supporting block for each pair of stationary contacts, said block having the plane of its major axis perpendicular to a vertical plane through the axis of said shaft, means to attach each pair of stationary contacts to their respective block on opposite sides of said shaft, and each block being formed to provide a plurality of shoulders at ,the respective ends .-thereof and between the contacts carried thereby, to thereby insure at least a predetermined minimum length of vertical insulating surface between said stationary contacts and between the same and said casing with the switch mounted in any of said positions.

10. A crane limit switch comprising, in combination with an oscillatable shaft, an operating lever oscillatably mounted concentric with said shaft and biased to a given position, a weight associated with said lever and normally exerting a force thereon opposing its normal bias and biasing it to another position, a cam on said shaft having a center apex, a double-ended supporting lever pivotally connected with said operating lever eccentric of its center of rotation, a roller on one arm of said supporting lever adapted to engage said cam to bias said shaft to either of its extreme positions of oscillation, an abutment on said operating lever, a coiled compression spring interposed between said abutment and the other arm of said supporting lever and arranged to urge said roller into contact with said cam, a guide member inside of said spring, said guide member being carried by said abutment and slidable through an orifice in said other arm of said supporting lever, said spring being composed of wire of such diameter 'and strength as to insure against telescoping of the coiled sections in the event of breakage of the spring at any point when in use, the aforementioned guide member cooperating, and the initial degree of compression of said spring when assembled being sufficiently great to afford the proper bias of said shaft to either of said extreme positions thereof in the event of such breakage.

l1. A crane limit switch comprising, in combination with an oscillatable shaft, an operating lever oscillatably mounted concentric with said shaft and biased to a given position, a weight associated with said lever and normally exerting a force thereon opposing its normal bias and biasing it to another position, a cam on said shaft having a center apex, a double-ended supporting lever pivotally connected with said operating lever eccentric of its center of rotation, a roller on one arm of said supporting lever adapted to engage said cam to bias said shaft to either of its extreme positions of oscillation, an abutment on said operating lever, a coiled compression spring interposed between said abutment and the other arm of said supporting lever and arranged to urge said roller into contact with said cam, a guide member inside of said spring, said guide member being carried by said abutment and slidable through an orifice in said other arm of said supporting lever, said spring being formed of wire of such diameter and strength and the initial degree of compression thereof when in assembled position being of such magnitude, and the pitch of the coils thereof being of such value, as to insure against telescoping of one section thereof into the other in the event of breakage of the same at any point when in use.

12. A crane limit switch for mounting with its operating shaft horizontal and for mounting in different positions about the axis of its operating shaft comprising, a metal casing completely enclosing the contact elements of said switch, an operating shaft oscillatably supported by said casing, a plurality of pairs of movable contacts mounted` on said shaft in insulated relationship thereto, the movable contacts of each pair being electrically connected with each other, a corresponding number of pairs of stationary contacts, one stationary contact of each pair being arranged for engagement simultaneously by the movable contacts respectively associated therependicular to a vertical plane through the axis of said shaft, means to attach each pair of stational-y contacts to their respective block on opposite sides of said shaft, an insulating supporting spacer interposed between each end of said block and said casing, means to attach said insulating block to said spacers, means to attach said spacers t0 said casing, each block being formed to provide a plurality of shoulders at the respective ends thereof and between the contacts carried thereby, and said blocks and said spacers acting to insure at least a predetermined length of vertical insulating surface between said stationary contacts and between the same and said casing with the switch mounted in any of said positions. t

" RICHARD B. HUNTER. 

